1. Field of the Invention
This invention relates generally to digital recording media and, more specifically, to a Flexible VCD Having Domed Center and Method of Making Thereof.
2. Description of Related Art
Portable storage of digital electronic data is a rapidly-developing field. The focus of the present invention is that of laser-readable (and writable) discs. Laser-readable disc types are generally Compact Discs (including CDs-prerecorded, CDRs-recordable, and CDRWs-rewritable) and Digital Video Discs (including DVDs-prerecorded, DVRs-recordable, and DVRWs-rewritable). Each of these disc designs and formats have similar basic structural configurations, as depicted in FIG. 1.
FIG. 1 is a perspective view of a conventional laser-readable disc 10. The conventional disc 10 has a plastic substrate 12 defined by a central spindle hole 14 formed therethrough. Standard CDs and DVDs have a substrate 12 defined by a 120 millimeter diameter 16 and a thickness 18 of 1.2 millimeters. While the standard disc 10 has a perimeter edge 20 that is circular, other shapes (and sizes) are readily available—of particular note is the business-card-sized disc. Data is stored on the disc via a laser readable (and optionally writable and rewritable) surface depicted here as the data storage area 21. The basics of the laser reading/writing technology will be discussed in connection with FIG. 2.
FIGS. 2A and 2B are partial cutaway side views of conventional compact and digital video discs, respectively. The conventional compact disc (CD, CDR, CDRW) 10A is defined by a substrate 12 having a thickness 18 that is 1.2 millimeters both at the perimeter edge 20 and at the central spindle hole 14. The substrate 12 is further defined by a top (recording) surface 22 and a bottom (read) surface 24. This is to say that the disc player/recorder's laser projects upwardly towards the disc substrate 12 from the bottom (at least in the depicted orientation). The laser light actually passes through the substrate 12 until it is reflected back by the bottom side of the top (recording) surface 22. The digital data is stored as a sort of texture on the top (recording) surface 22; the texture effects the way in which the laser light is reflected back down to the laser reader, which is interpreted as data in a standardized format. Of course other important elements are a part of CDs and DVDs, such as the type of reflective coating applied to the recording surface (which can determine whether the disc is rewritable or recordable), as well as any decorative films or colorations applied above that.
FIG. 2A depicts the structure of a conventional digital video disc (DVD, DVR, DVRW). The conventional DVD is actually comprises of two thin discs bonded together. While the overall disc thickness 18 is 1.2 millimeters at the perimeter edge 20 and the spindle hole 14, this overall substrate thickness is actually made up of a top substrate element 12A bonded atop the bottom substrate element 12B. The bottom substrate element 12B is actually the data-storing portion of the disc 10B. The top (recording) surface 22 is actually the top surface of the bottom substrate element 12B. Of course, the bottom (read) surface 24 is the bottom surface of the bottom substrate element 12B. The bottom substrate element 12B has a disc thickness of 0.6 millimeters, which means that the depth of the disc as read by the laser is only 0.6 millimeters.
The top substrate element 12A, which is also 0.6 millimeters thick, provides really no functional benefit to the disc 10B beyond making it stiffer than the bottom substrate 12B alone would be, and further providing the additional thickness necessary to provide an overall disc thickness 18 of 1.2 millimeters.
A critical aspect of the configuration of CDs and DVDs is the thickness of the disc substrate directly adjacent to the spindle hole 14. When a disc is loaded for playing/recording in a disc player, the player will actually clamp down on the disc over the spindle hole 14. The player will then conclude by that the disc top surface 22 or 26 is at the same level as the top of the disc clamp. The laser will then be energized to determine the disc depth/thickness to the top (recording) surface 22. In the case of a CD 10A, the player/recorder will detect a depth of 1.2 millimeters, while in the case of a DVD 10B, the player/recorded will detect a depth of 0.6 millimeters. This detected depth is a way for the player/recorder to confirm whether the disc is a CD or a DVD. As such, conventional CD and DVD players and recorders rely upon the thickness of the disc under the disc clamp (in the player) to determine whether a CD or a DVD is being read. If there is a non-standard depth, or a non-standard disc thickness 18 adjacent to the spindle hole 14, the error will prevent the disc from being reliably read on all player/recorders.
As discussed above, the extra substrate element included with a conventional DVD is not involved in the actual data recording and reading (at least beyond giving the player its initial focus check). There are, however, limitations to the usefulness of the DVD introduced because of this extra thickness. First, if the DVD was thinner (i.e. 0.6 millimeters), it would be flexible. A flexible DVD could be very popular in the context of mass mail advertising (such as in magazines); now the discs have to remain flat. Furthermore, the second substrate is simply wasted material; its elimination would be cost effective and more environmentally conscious. Finally, less material will reduce mold processing time as well as eliminating a production step involving the bonding of the top substrate element 12A to the bottom substrate element 12B.